The present invention relates to xe2x80x9cdescendersxe2x80x9d for use in abseiling.
Abseiling is a technique used to descend steep surfaces such as cliff faces and is often used by persons involved in activities such as mountain climbing, canyoning and caving. In order to abseil down a cliff face, one end of a rope is made fast at the top of the cliff and the person making the descent then slides down the rope. The rope is passed either around the body of the person or more usually through a descender attached to a harness worn by the person such that the passage of the rope around the body or through the descender provides sufficient friction to slow the rate of descent to a safe speed.
A descender comprises rope engaging surfaces around and between which the rope travels, along a tortuous path, to provide frictional engagement between the rope and the descender. The rate of descent is normally controlled by holding the free or tail end of the rope to control the tension on the rope where it emerges from the descender and thereby to control the degree of frictional engagement between the rope and the descender which in turn controls the rate of descent.
Descenders used in abseiling vary greatly in performance and complexity, there being a variety of relatively simple devices which rely on frictional engagement between the rope and metal rings or racks about which the rope is wrapped, and a number of more complex descenders which incorporate a braking mechanism which allows the friction between the rope and the descender to be varied other than by simply controlling the free or tail end of the rope. The earliest of these more complex devices had a handle or lever which when operated tended to increase the friction between the descender and the rope. This type of descender was not a great improvement over the more simple devices as the brake was not self-engaging and therefore, if the user was knocked unconscious, he would fall in the same way as the user of the earlier devices.
An improved type of descender was disclosed in U.S. Pat. No. 4,596,314 to the present applicant which provides a descender having a simplicity of construction and operation which was not achieved by earlier prior art descenders. The descender disclosed in that application provided a variable braking action which increased when a handle was released. Therefore if the user was knocked unconscious and released the handle, the user""s fall would be braked.
A disadvantage of the descender disclosed in U.S. Pat. No. 4,596,314 is that the actuation and release of the self-engaging brake can in some situations be rather abrupt or jerky. For example, it can be difficult for to inexperienced users to smoothly control the braking action.
U.S. Pat. No. 5,597,052 (also to the present applicant) provided a modification to the descender shown in U.S. Pat. No. 4,596,314 comprising a variable braking mechanism operated by a lever which allows the user to smoothly control the braking action and thereby avoid or minimise the jerkiness which can be experienced with the use of this known type of descender.
The present invention provides further safety improvements in descenders, in particular, but not exclusively, to the descender of the type described in U.S. Pat. No. 5,597,052.
The present invention provides a descender for use in abseiling comprising:
a base having a connection means for connection to a harness or the like:
a pivotal member pivotally mounted on the base about a pivot axis extending generally normal thereto, the pivot axis being spaced from the connection means;
the pivotal member having first and second spaced projections for engaging a rope, the projections both extending generally parallel to the pivot axis with the first projection being disposed generally about the pivot axis and the second projection being located substantially on the opposite side of the pivot axis with respect to the connection means;
the base further having a stop means located adjacent the second projection and a lever pivotal about a pivot extending through or located adjacent to the stop means, one end of the lever defining a handle pivotable in an arcuate path between first and second end positions; and
wherein the pivotal member and the other end of the lever define complementary displacing formations the formations being shaped and configured such that as the lever travels in its arcuate path about the pivot, they regulate the distance between the stop means and the second projection whereby, in use, a rope passing around and between the first and second projections and between the second projection and the braking surface will have a resistance force applied to it which is a minimum when the second projection is moved away from the stop means by actuating the lever to cause the complementary displacing formations to contact one another and thus decrease the braking and friction forces on the rope as it passes between the second projection and the stop means and is at a maximum when the lever moves to either end position of its arcuate path wherein the rope is pressed between the second projection and the braking surface.
A first important advantage of the invention is that the lever is inherently safe as braking is at a maximum if the lever is moved to either extreme end position. Any one panicking would tend to force the lever to one side which would result in maximum braking.
A second advantage is that in manipulating the handle of U.S. Pat. No. 4,596,314 and U.S. Pat. No. 5,597,052, can be difficult when the descender is used to lower heavy loads, particularly loads approaching 500 kg or more. The handle has a short arc of travel and this does not allow continuous control but rather provides somewhat jerky movement of the load. In contrast the lever of the present invention has a greater arc of movement and provides better control adjustments when lowering heavy loads and can be used to control heavier loads of 200 kg or more with relative ease.
In one embodiment the complementary displacing formations comprise a cam surface defined on the other end of the lever and the pivotal member defines a cam follower surface.
The cam surface is typically a relatively thin plate which allows the rope to pass over it. The stop member is preferably co-axial with the pivot and may typically be generally cylindrical. This structure has cost advantages over the forged cam of U.S. Pat. No. 5,597,052. Further it can adjust the distance between the stop member and the second projection effectively reducing the drag/friction on the rope when the lever is in a mid-position.
In an alternative embodiment the cam surface is defined on the pivotal member and the cam follower is locate on the other end of the lever. The cam follower may be an annular ring which is free to rotate about its central axis.
In one embodiment, the pivotal member also has a handle means to selectively pivot the pivotal member relative to the base. In this embodiment in use, a rope passing around and between the first and second projections and between the second projection and the braking surface will have a resistance force applied thereto which is at a minimum when the second projection is selectively moved away from the stop by actuating the handle means, and is at a maximum when the handle means is released and the tension of the rope causes the second projection to bear against the stop and press the rope between the braking surface and the second projection and thereby create an additional braking force.
Preferably, the lever has a retention means at a position spaced from the cam and through which, in use, a tail of the rope passes after emerging from between the second projection and the braking surface so that the lever will move with the tail of the rope and may be actuated by changing the position of the tail of the rope relative to the descender. Preferably, the retention means is in form of a pair of recesses in the lever through which, in use, the tail of the rope is threaded.
Preferably, the first and second projections define sheaves which are fixed relative to the pivotal member.